In the production of tubular steel couplers for joining opposing end portions of two concrete reinforcing rods, commonly referred to as xe2x80x9crebarsxe2x80x9d, for example, of the general type disclosed in U.S. Pat. Nos. 3,415,552, 3,551,999 and also U.S. Pat. No. 5,664,902 which issued to the assignee of the present invention, it is common to purchase seamless steel tubing and cut the tubing into sections. The opposite end portions of the tubing sections may be formed with internal threads, for example, as disclosed in U.S. Pat. No. 3,415,552, or the opposite end portions of a tubing section may be compressed or swaged radially inwardly onto the corresponding opposing end portions of the reinforcing bars, for example, as disclosed in U.S. Pat. No. 3,551,999. While the steel tubing usually has a generally cylindrical inner and outer surfaces, the inner surface may be machined with internal threads or with internal axially spaced circumferential teeth, as shown in the aforementioned patents. The cylindrical tubing may also be formed between dies to produce a tubular coupling body having non-cylindrical outer and/or inner surfaces, for example, as disclosed in above mentioned U.S. Pat. No. 5,664,902.
Since the cost of producing seamless steel tubing is substantially more than the cost of producing solid steel cylindrical bars or rods, tubular rebar coupler bodies have also been produced by machining sections of solid steel bar stock, preferably on a computer controlled lathe or machining center. A bore is first drilled within each solid rod section and then internal threads are machined within the bore. It is also known to machine one end portion of a solid coupler body to form an end portion of reduced diameter and on which external threads are then machined.
The end portion of the coupler body having the drilled bore is secured to an end portion of a concrete reinforcing bar by compressing or swaging the end portion radially with a mechanical or hydraulic press so that the coupler body positively grips the concrete reinforcing bar and provides the bar with an externally threaded end portion. The machined external and internal threads may be generally cylindrical or tapered, depending on the application of the rebar coupler. The primary disadvantage of machining solid steel bar stock or rod is the production of waste or scrap material which adds significantly to the cost of producing the rebar couplers.
The present invention is directed to an improved method of producing or making steel couplers for joining opposing end portions of concrete reinforcing bars or rebars and which significantly reduces the cost of producing couplers with tubular end portions. In accordance with the invention, a section of solid steel rod is placed within the cavity of a first die member with an end surface of the rod section facing or opposing a bottom end surface of the cavity. A male die or punch is forced axially downwardly or into the solid rod section to form or cold-forge a bore within an end portion of the rod section and to extrude the steel axially in a reverse direction to form a first tubular end portion of a coupler body.
In order to form an internally threaded bore within an opposite end portion of the coupler body, the rod section with a bore in one end portion is placed within another die member defining a second cavity with an inwardly or upwardly projecting punch. The punch projecting downwardly from the moveable die is forced into the bore to cold-forge or extrude the steel into the annular cavity surrounding the bottom die punch and to form a second bore and again to cause a reverse flow of the steel to extend the length of the first bore and the first tubular portion of the coupler body. After the coupler body is removed from the second die member, the bore within the second end portion is internally threaded.
A tubular coupler body having a tubular end portion and a reduced opposite end portion with external threads is formed by inserting a solid rod section into a die cavity having a reduced inner end portion. When the punch on the moveable die is forced axially into the solid rod section to form the first bore and tubular body end portion, the steel extrudes partially into the smaller portion of the cavity. A second step of the cold forging operation completes the reduced diameter solid end portion which is externally threaded.
A coupler body having opposite tubular end portions with an internal radial wall is also formed in accordance with the invention by inserting a solid rod section into a cylindrical cavity of a first die member and forcing a punch with a ram of a hydraulic press into the solid rod section to form partially a first tubular end portion defining a bore. The rod section is then inverted and placed within a cavity of a second die member having a punch projecting inwardly into the first bore. The ram punch is then forced into the solid end portion of the rod section to form or cold-forge the second tubular end portion of the coupler body and to define an integral center wall separating the bores within the opposite end portions of the coupler body. After opposing end portions of two concrete reinforcing bars or rebars are inserted into the bores of the coupler body, the opposite tubular end portions of the body are compressed or swaged inwardly to form positive connections with the rebars.